I  II 

001 


RLF 


INDEX 


PAGE. 

Introduction  to  Krom's  Improvements  in  Ore  Crushing  and 

Concentrating  Machines,  etc.,  etc.,  etc.,     -  -       3 

Notice  to  In f ringers,     -  4 

Krom's  Original  Sectional  Ore  Breaker,    -  -       5 

"       Improved       "  7 

Rolling  Toggle  (enlarged  view),  -       8 

Krom's  Original  Steel  Crushing  Rollers,       -  9 

"       Second  Improved  Steel  Crushing  Rollers,     -  11 

Endorsement  of  Prof.  Alex.  Trippel,    -  12 

Krom's  Third  Improved  Steel  Crushing  Rollers,  -     14 

Housing  for  Krom's  Rollers,  16 

Endorsements  of  Krom's  Belt  Rollers,      -  -     17 
Krom's    Fourth    Improved   (Swinging    Pillow-Blocks)    Steel 

Crushing  Rollers,  -  19 

Rollers  and  Stamps  compared,  -     22 
Stetefeldt's  comparison  between  Krom's  Rollers  and  the  Stamp 

Battery,  27 
Additional  Endorsements  by  R.  D.  Clark,  Esq.,  32 
Closing  remarks  of  the  Author,    -  33 
Theoretical  Treatise  on  Krom's  System  of  Pneumatic  Concen- 
tration of  Ores,  -     35 
Endorsements  of  the  System,  40 
Description  of  the  Pneumatic  Jig,    -  -     46 
Laboratory  Crusher  and  Rollers,  54 
Krom's  Dry  Kiln,  56 
"        Revolving  Screen,  60 


COLLEGE  of  MINING 

DEPARTMENTAL 
LIBRARY 


BEQUEST  OF 


SAMUELBENEDICTCHRISTY 

PROFESSOR  OF 

MINING  AND   METALLURGY 
1885-1914 


KROM'S  ORE  CRUSHING  AND  CONCENTRATING  MACHINES, 


S.  R.  KROM,  ENGINEER, 

n 

AND    MANUFACTURER    OF 

ORE   BREAKERS    (STEEL  SECTIONAL), 
STEEL   CRUSHING  ROLLS, 

PNEUMATIC    CONCENTRATORS, 
REVOLVING    SCREENS, 
GRAVITY   DRY   KILNS  AND   ORE   FEEDERS. 


LABORATORY    CRUSHERS, 
LABORATORY    ROLLS, 

LABORATORY  CONCENTRATORS, 
LABORATORY    SCREENS. 


Plans  for  Lixiriation  and  Concentration  Works, 


Received  the   Highest  Award   from   the   U.  S.    Centennial 
Commission  for  the   Pneumatic  Concentrator. 


YOPtKl. 

1885. 


K-i.1 

~YY\ 

' 


KROM'S    IMPROVEMENTS 

IN 

ORE  CRUSHING  AND  CONCENTRATING  MACHINES, 

Etc.,    Etc.,    Etc. 


In  connection  with  perfecting  a  system  of  pneumatic  concen- 
centration,  I  had  in  view  the  improvement  of  machines  for  crushing 
and  pulverizing  ores.  A  study  of  the  whole  subject  convinced 
me,  that  the  principle  upon  which  the  construction  of  the  Blake 
Crusher  and  that  of  the  rollers  are  based,  possessed  the  mechanical 
elements,  which,  if  perfected  and  simplified,  would  make  these 
machines  the  successful  rivals  of  every  other  device.  It  is  well 
known,  that  until  very  recently,  the  stamp  battery  held  undisputed 
possession  of  the  field,  and  mill  men  as  well  as  mill  builders,  almost 
universally,  believed  that  stamps  would  not  be  superseded  by  any 
other  machine  for  fine  crushing. 

The  first  step  to  drive  stamps  from  the  field,  was  the  introduction 
of  rollers  in  the  Bertrand  and  the  Mt.  Cory  Mills.  In  both  of 
these  mills,  the  great  superiority  and  economy  of  a  system  of 
crushing  with  rollers  instead  of  stamps  has  been  fully  demonstrated. 

While  perfecting  the  rollers  I  had  the  fact  confronting  me,  that 
they  had  frequently  been  tried  without  success.  In  fact,  the 
universal  opinion  prevailed  that  rollers  could  be  used  only  for  coarse, 
and  not  for  fine  crushing.  The  secret  of  the  difficulty,  I  discovered 
to  be  in  the  imperfect  and  weak  character  of  the  rollers  heretofore 
used,  due  to  a  misconception  of  the  requirements  for  a  machine  for 
such  work,  and  a  failure  to  appreciate  the  advantages  of  continuous 
rolling  crushing  surfaces,  operating  on  the  toggle  lever  principle, 
which  gives  the  greatest  crushing  pressure  with  the  least  power 
expended,  and  the  minimum  of  wear. 


But  no  sooner  is  the  fact  established  that  rollers  are  destined  to 
supersede  stamps,  than  some  persons  jump  to  the  conclusion  that 
cheap  rollers  will  also  prove  successful,  and  manufacturers  of  cheap 
machines  are  making  statements  that  they  sell  rollers  at  one-half 
the  price  of  my  improved  steel  rollers,  which  will  do  the  same 
work.  Those  who  believe  such  statements  and  buy  such  cheap 
rollers,  will  pay  dear  for  their  experience. 

It  is  the  great  strength  of  my  rollers,  superior  material  used,  perfect 
workmanship,  completeness  and  simplicity  of  design,  which  makes 
them  a  success  and  so  economical ;  and  no  one  understanding  the 
subject  will  consider  the  price  too  high  for  the  quality  of  the 
machines.  As  an  aid  to  legitimate  mining  enterprise,  it  has  been 
my  aim  to  perfect  a  system  of  machinery  for  milling  and  con- 
centrating ores,  and  to  make  such  machinery  a  standard  of 
excellence.  The  advantage  and  economy  of  employing  the  best 
which  can  be  produced,  is  becoming  slowly  but  better  understood. 

S.  R.  KBOM. 


NOTICE. 


Some  manufacturers  are  making  ore  breakers  and  crushing 
rollers  which  infringe  on  my  patents.  Purchasers  of  such  machines 
are  notified  that  they  will  be  held  equally  liable  for  damages  as 
the  manufacturers. 

All  the  machines,  either  ore  breakers  or  crushing  rollers  which 
have  tie  bolts  to  take  the  strain  due  to  crushing,  are  infringements 

on  my  patents. 

S.  R.  KROM. 


ORE   BREAKERS. 

Every  one  who  has  any  knowledge  of  ore  crushing 
machinery  is  so  familiar  with  the  Blake  Crusher  and  its 
construction,  that  no  cuts  or  description  of  it  is  neces- 
sary here.  But  during  the  life  of  the  patent  (21  years) 
of  this  celebrated  and  valuable  machine,  the  frame  was 
cast  in  one  piece,  and  no  improvement  of  any  im- 
portance was  made  in  the  machine  until  after  the  patent 
had  expired. 

Fig.    1. 


KROM'S  ORIGINAL  PATENTED  SECTIONAL  ORE  BREAKER. 

Re-issued  April  llth,  1882. 


The  first  practical  plan  to  improve  the  construction 
of  the  Blake  Crusher  is  shown  in  cut,  Fig.  1,  and  was 
patented  in  1875.  The  principal  features  covered  by 
the  patent  granted  for  this  machine  (Fig.  1)  are  the  tie 
bolts  to  take  the  strain  due  to  crushing,  and  breaking- 
cups  to  relieve  the  machine  from  excessive  strain.  The 
breaking-cups  are  placed  on  the  tie-bolts  and  also  on  the 
pitman,  but  it  is  intended  that  the  small  cups  on  the 
pitman  should  be  the  weakest  and  only  these  give 
awray.  A  lug  underneath  the  pitman  holds  it  from 
dropping  too  low.  This  method  of  constructing  a 
crusher  with  bolts  not  only  makes  a  stronger  machine, 
but  one  of  less  weight,  and  easier  to  transport,  and  allows 
the  employment  of  means  to  prevent  the  machine  from 
being  subjected  to  undue  strain. 


Fig.  2. 


KROM'S  IMPROVED  PATENTED  STEEL  SECTIONAL  ORE  BREAKER. 

Covered  by  Re-issued  Patent,  April  llth,  1882,  and  Patent  allowed  for  improvements. 


The  next  steps  in  improvements  are  shown  in  the  cut, 
Fig.  2.  In  this  machine  the  upper  tie-bolt  is  shortened 
so  as  to  give  a  better  and  more  convenient  form  to  the 
side  frame,  and  the  lower  tie-bolt  is  so  placed  that  it 
receives  all  the  strain  due  to  crushing  the  ore.  In  the 
toggle  abutment,  through  which  the  main  tie-bolt 
passes,  are  recesses  around  the  bolt  holes,  and  these 
recesses  are  covered  with  wrought  iron  washers  of 
sufficient  strength  so  they  will  not  bend  under  the 
ordinary  strain  in  crushing  the  ore,  but  yield  to  ex- 


Fig,  3. 


KROM'S  IMPROVED  PATENTED  STEEL  SECTIONAL  ORE  BREAKER. 

Covered  by  Ke-issuecl  Patent  April  11,  1882,  and  Patent  allowed  for  improvements. 


8 


cessive  strain.  These  washers  take  the  place  of  the 
breaking  cups  in  the  first  machine,  but  do  not  fly  to 
pieces,  and  therefore  both  ends  of  the  toggle  block  yield 
evenly  together,  and  the  frame  of  the  machine  is  not 
liable  to  be  twisted  or  broken,  or  the  bolts  bent. 

The  third  improvement  is  in  forming  the  crushing 
faces  of  bars  of  steel,  and  in  the  means  of  clamping 
them  securely  in  place.  These  bars  are  of  good 
steel,  rolled  to  standard  sizes,  and  cut  to  proper  lengths. 
The  lower  bars  are  hardened  to  increase  their  durability. 
Provision  is  made  for  bringing  the  jaws  closer  together 
to  compensate  for  wear.  Thin  strips  of  metal  are  also 
provided  to  put  behind  the  bars  to  keep  the  wearing 
faces  in  line.  The  bars  or  crushing  faces  can  easily  be 
got  at  by  taking  the  nuts  from  the  bolts,  and  sliding 
the  stationary  jaw  forward.  The  fourth  improvement 
consists  in  hanging  the  jaws  on  an  axis  below  the  crushing 
faces  instead  of  at  the  top  as  in  the  Blake  Crusher. 
This  manner  of  hanging  the  movable  jaw  gives  a  more 
uniform  product,  and  the  principle  is  correct,  as  the 
strain  on  the  jaw  is  greater  at  the  bottom  than  at  the 
top,  and  consequently  the  motion  should  be  the  least 
where  the  strain  is  the  greatest. 

The  fifth  improvement  consists  inj  the^employment  of 
toggles  with  rolling  ends  which  work  without  friction  or 
oil.  In  this  cut  the  teeth  which  hold  ^the  \ 

toggles  in  place  are  omitted  on  one  end  so 
as  to  better  show  the  rolling  surfaces. 


ROLLING  TOGGLES. 


The  bearings  are  self-adjusting,  large  and  long,  and 
the  machine  is  constructed  for  high  speed,  hard  work  and 
large  crushing  capacity. 


10 


CRUSHING   ROLLERS. 

Fig.  4,  represents  the  first  step  in  the  improvement 
of  crashing  rollers  constructed  with  bolts  to  take  the 
strain.  It  is  also  the  first  crushing  machine  with  forged 
steel  tires.  The  system  of  gearing  is  also  new,  and  an 
improvement  on  anything  before  or  since  it  was  intro- 
duced. It  will  be  observed  also  that  the  pillow  blocks 
are  well  adapted  to  take  the  strain.  It  is  the  first 
machine  of  the  kind  carried  on  a  bed  plate  in  one  piece. 
Breaking  cups  are  also  introduced  to  relieve  the  machine 
from  undue  strain.  This  is  the  first  time  that  such  a 
device  was  introduced  in  crushing  machines.  The 
patent  granted  for  these  rollers  covers  the  bolts  to  take 
the  strain,  the  system  of  gearing,  the  manner  of  putting 
on  the  steel  tires  and  the  breaking  cups.  Some  of  the 
details  in  this  cut  are  omitted  as  not  being  essential 
here,  but  will  appear  in  the  next  machine. 


Fig.  5. 


.SIDE-VIEW 


KROM'S   SECOND   IMPROVED    STEEL   CRUSHING  ROLLERS. 

Covered  by  patent  July  16th,  1872,  and  patents  allowed  for  improvements. 


11 


The  next  step  in  the  improvement  of  crushing  rollers 
is  shown  in  cuts,  Figs.  5  and  6.  It  consists  of  a  recon- 
struction of  the  pillow  blocks  so  as  to  adapt  them  to 
one  bolt  on  each  side  instead  of  two,  as  in  the  previous 
cut,  Fig.  4.  This  at  once  simplifies  the  machine,  and  in 
other  respects  makes  a  better  pillow  block.  The  bolts 
being  placed  close  to  the  bearings  serve  the  purpose 


Fig,  6. 


-END-VIEW- 


KROM'S   SECOND   IMPROVED   STEEL   CRUSHING   ROLLERS. 

Covered  by  patent  July  16th,  15T2,  and  patent  allowed  for  improvements. 

better  than  four  bolts,  two  bolts  being  much  more  con- 
venient for  adjusting  the  rollers. 

This  arrangement  also  allows  the  shafts  to  be  lifted 
out  of  their  bearings  for  repairs  without  removing  any 
of  the  tie-bolts,  and  permits  the  use  of  springs  on  the 
tie-bolts,  as  shown  at  S,  Fig.  5.  It  is  not  practicable  to 


12 


use  springs  with  four  bolts.  These  springs  were  intro- 
duced to  supersede  the  breaking  cups  in  Fig.  4.  The 
tie-bolts  have  solid  collars  near  the  middle,  and  a  nut  on 
each  end.  The  springs  and  pillow  blocks  are  placed 
between  the  collar  and  nut,  so  that  the  pressure  is  obtained 
without  forcing  the  rollers  together  when  the  springs 
are  set  up  to  give  the  necessary  resistance  to  crush  the 
ore.  At  the  date  of  this  machine  it  was  considered 
necessary  to  employ  some  means  to  relieve  the  machine 
from  undue  strain;  and  the  springs  as  here  shown  are 
the  best  arrangement  for  the  purpose  yet  devised.  The 
arrangement  of  the  gearing  is  the  same  as  in  Fig.  4, 
except  that  the  intermediate  gear  D1  is  increased  in  size, 
and  so  placed  as  to  require  no  change  of  position  when 
the  pillow  blocks  are  moved  up  to  adjust  the  distance 
of  the  rollers,  and  to  compensate  for  wear.  The  wheel 
D1  is  placed  nearly  on  a  line  drawn  perpendicular 
through  wheel  B2,  but  two  inches  in  front  of  it;  and 
when  the  tires  are  worn  out  the  wheel  D1  will  be  two 
inches  in  the  rear  of  the  perpendicular  line  through 
wheel  B2.  This  movement  of  four  inches,  when  so 
divided,  only  slightly  affects  the  meshing  of  the  teeth  of 
the  wheels  D1  and  B2,  the  variation  being  only  -^  of  an 
inch  from  a  true  pitch.  It  will  be  seen  that  one 
roller  is  driven  through  the  intermediate  wheel  D1,  and 
the  other  roller  by  a  pinion,  C1,  directly  engaging  with 
wheel  B1.  By  this  arrangement  and  location  of  wheel 
D1  the  rollers  can  be  adjusted  without  change  of 
position  of  any  of  the  gear.  In  the  machine  shown  in 
Fig.  4,  it  was  necessary  to  adjust  gear-wheel  D1,  as  the 
gear-wheel  B2  was  moved  forward  toward  gear-wheel  B1 . 
It  was  of  these  rollers  that  Prof.  Alex.  Trippel  spoke 
when  he  said — uThe  steel  rollers  of  Mr.  Krom's  are 
exceedingly  well  constructed.  They  are  undoubtedly 
the  finest  ever  made,  well  proportioned,  and  very 


13 


powerful.  *  '"  An  important  fact  which  was 

developed  on  this  trial,  was  the  apparent  practicability 
and  advantage  in  substituting  a  system  of  crushing  by 
steel  rollers  for  stamp  batteries." 

(The  above  is  from  U.  S.  Commissioner  Raymond's 
report  of  1876.) 

It  was  the  success  of  these  geared  steel  rollers  at  the 
Galena  Mills,  Nevada,  that  led  to  the  adoption  of  the 
improved  form  at  the  Bertrand  Mill  at  Geddes,  Nevada, 
as  described  below. 


14 


Fig.   7. 


SIDE  VIEW 


KROM'S  THIRD  IMPROVED  STEEL  CRUSHING   ROLLERS. 

Covered  by  patent  July  16th,  1872,  and  patent  allowed  for  improvements. 


Figs.  7  and  8  illustrate  very  important  additional 
improvements  in  crushing  rollers.  The  1st  is  the  sub- 
stitution of  band  wheels  for  toothed  gearing.  2d.  The 
substantial  casing  for  inclosing  the  rollers,  and  a  hopper 
to  insure  the  spreading  of  the  ore  evenly  across  the  face 
of  the  rolls.  These  improvements  complete  the  adap- 


15 


tation  of  rollers  for  pulverizing  ores  to  any  degree  of 
fineness  required.  With  pulleys  we  can  run  at  any 
speed  desired,  and  thereby  increase  the  capacity  of  the 
rollers.  The  wear  is  reduced  nearly  to  the  crushing 
faces  alone.  The  danger  of  breaking  the  machine  is 
avoided,  and  the  rollers  perform  their  work  with  but 
little  noise  and  shock. 


Fig.   8. 


END      VIEW 


KROM'S  THIRD  IMPROVED  STEEL  CRUSHING   ROLLERS. 

Covered  by  patent  July  16th,  1872,  and  patent  allowed  for  improvements. 


HOUSING  FOR  KROM'S  PATENTED  STEEL  CRUSHING  ROLLERS. 

The  housing  (Fig.  9)  so  incloses  the  rollers  that  the 
dust  made  in  crushing  is  easily  prevented  from  escaping 
into  the  building  by  means  of  a  small  draught  of  air 
produced  by  an  exhaust  fan.  The  housing  also  forms  a 
very  substantial  frame  for  supporting  the  cheek  pieces 
and  the  feeding  hopper.  I  prefer  to  drive  with  one 
large  pulley,  and  use  the  small  one  to  insure  the 
bite  of  the  rollers  upon  the  ore.  Both  rollers  of  course 
when  crushing  travel  at  the  same  surface  speed,  but  I 
prefer  to  speed  them  so  that  the  roller  driven  by  the 
small  pulley,  when  the  machine  is  not  crushing,  will 
revolve  one  or  two  revolutions  faster  per  minute.  The 


17 


reasons  for  preferring  this  system  of  driving  with  only 
one  large  pulley,  are  : 

1st.  It  would  not  be  a  good  arrangement  to  hang 
on  the  movable  pillow  block,  so  large  and  heavy  a 
pulley  as  would  be  required. 

2d.  The  driving  of  one  roller  will  cause  the  other 
to  revolve  at  the  same  surface  speed,  where  hard  ore  is 
fed  between  them,  and  therefore  it  is  only  necessary 
to  'drive  one  roller  with  a  strong  and  steady  power, 
and  the  other  with  sufficient  force  to  insure  the  rollers 
always  taking  hold  of  the  ore,  and  to  keep  the  same  in 
motion  during  the  time  when  no  ore  is  between  them. 

In  reference  to  these  rollers  Mr.  Stetefeldt  said,  be- 
fore their  success  had  been  practically  demonstrated : 

"  I  am  firmly  convinced  that  Krom's  Improved  Steel 
Rollers,  if  they  are  given  a  fair  trial,  will  make  stamps 
a  thing  of  the  past.  *  *  *  *  * 

It  is  Mr.  Krom's  merit  to  have  constructed  rollers 
which  reduce  ores  to  any  degree  of  fineness.  The 
splendid  results  at  the  Geddes  Mill,  Nevada,  have 
established  the  fact  beyond  any  question.  It  is  not  too 
much  to  say  that  rollers  produce  the  same  results  as 
the  stamp  batteries,  with  one-half  the  power  and 
one-half  the  expense  in  wear,  leaving  their  much  lower 
original  cost  out  of  the  question." 

Mr.  Albert  Arents,  Superintendent  of  the  Mt.  Gary 
Mill,  says  :  "Now  as  to  the  economical  question,  the 
only  one  of  practical  interest,  I  will  state  that  the  cost 
of  treating  a  ton  of  ore  at  the  Bertrand  Mill  is  thirty 
per  cent.  (30$)  cheaper  than  at  the  Northern  Bell  Mill 
(a  stamp-mill),  although  the  latter  is  crowded  to  its 
utmost  capacity,  and  treats  more  ore  than  any  other  mill 
of  its  size  I  know  of.  *  *  *  *  *  I  once  advised 
having  a  side  motion  to  one  of  the  rollers,  but  I  find 
if  they  are  fed  even  the  rollers  wear  even.  I  am 


18 


astonished  at  the  even  degree  of  wear  of  the  steel  tires. 
I  would  not  use  stamps  now  for  our  purpose  under  any 
considerations." 

Mr.  R.  D.  Clark,  Superintendent  of  the  Bertrand 
Mining  Co.,  says :  "  One  great  reason  of  our  cheap 
milling  at  the  Bertrand  is  that  we  use  rollers  instead  of 
stamps.  We  crushed  about  15,000  tons  of  ore  before 
putting  new  tires  on  the  finishing  rollers,  and  have 
crushed  in  all  about  20,000  tons,  and  we  do  not  expect 
to  put  new  tires  on  the  roughing  rollers  for  two  or 
three  months  yet.  From  my  experience  the  past  four- 
teen (14)  months,  it  is  safe  to  calculate  that  each  set  of 
tires  and  each  set  of  phosphor  bronze  linings  will 
last  to  crush  20,000  tons  of  ore.  There  has  been  no 
other  expense  for  repairs  upon  our  rollers  except  the 
cheek  pieces.  The  faces  of  the  worn-out  tires  are  not 
grooved  at  all,  and  they  would  be  still  good  for  wear 
had  they  not  expanded  by  becoming  worn  thin.  They 
have  certainly  stood  the  test  of  time,  and  are  to-day 
more  in  favor  with  us  than  ever  before.  We  would 
not  have  stamps  if  furnished  without  cost,  and  kept  in 
repair  for  nothing  also." 

Additional  testimony  from  an  experienced  mill  man : 
"  I  have  been  an  advocate  of  stamps,  but  after  seeing 
the  quantity  of  ore  your  rollers  have  crushed  at  the 
Bertrand  Mill  (30,000  tons),  I  am  convinced  of  their 
superiority  over  stamps,  and  have  decided  to  use  them 
in  my  new  mill. 

SIMEON  WENBAN, 

COETEZ,  NEVADA." 

Much  more  could  be  added  in  the  way  of  favorable 
comments  in  relation  to  steel  rollers  of  the  kind  shown 
in  the  cut  and  just  described  in  Figs.  7,  8  and  9,  but 
further  quotations  would  be  unnecessary  here,  since  the 


19 


testimonials  above  are  quite  full,  and  come  from  persons 
widely  and  favorably  known  as  the  most  skillful  in  the 
profession  of  mill-men  and  metallurgists. 


Fig.    10. 


SIDE  VIEW  OF  KROM'S  FOURTH  IMPROVED  STEEL  CRUSHING  ROLLERS. 

Patented  July  16th,  1872,  and  patent  for  improvements  pending. 


20 


The  next  and  latest  step  in  the  improvement  of 
crushing-rolls  is  the  swinging  pillow-blocks,  shown  in 
Figs.  10  and  11.  This,  by  reason  of  its  uniqueness  and 
importance,  deserves  to  rank  first  in  the  order  of  merit, 
In  all  other  machines  one  pair  of  the  pillow-blocks  are 
arranged  to  slide  on  the  bed-plate,  and  each  one  of  the 
sliding  pillow-blocks  has  to  be  adjusted  separately.  It 
requires  care  to  bring  up  the  two  movable  pillow-blocks 
evenly  and  parallel  with  the  stationary  ones ;  and  any 
looseness  between  the  faces  of  the  movable  pillow-blocks 
and  the  bed-plate  results  in  damage  to  the  faces  and 
pounding  on  the  bed.  In  this  machine  all  the  bearings 
are  securely  and  firmly  fixed  to  the  bed-plate,  and  no 
chance  whatever  exists  for  looseness,  causing  wear  or 
damage  to  any  part  of  the  machine.  (In  fact,  the 
movable  bearings  are  now  better  secured  to  the  bed- 
plate than  the  stationary  ones,  although  the  latter  are 
very  securely  bolted  on  the  bed.)  The  two  swinging 
bearings  are  united  together  by  a  very  heavy  shaft 
(???,  Fig.  11)  11  inches  in  diameter,  so  that  the  bearings 
must  swing  together,  and  consequently  the  rollers  and 
shafts  are  always  parallel.  The  shaft  m,  connecting  the 
swinging  bearings,  is  so  strong  that  one  bolt  on  one  side 
is  sufficient  to  hold  the  rolls  together  when  crushing  ore. 
It  will  be  observed  that  springs  have  been  dispensed 
with.  The  machine  is  constructed  so  strong  that  they 
are  no  longer  required ;  and  besides  I  now  employ 
magnets  to  take  out  from  the  ore  all  pieces  of  steel 
which  might  dent  the  faces  of  the  rollers. 

The  rolls  work  better  and  more  economically  without 
springs.  Contrary  to  what  might  at  first  be  expected, 
the  machine  is  more  simple  than  any  other  and  more 
durable.  The  tires  are  held  by  two  heads  slightly  cone- 
shaped.  One  of  these  heads  is  securely  fixed  to  the 
shaft  by  shrinking  it  on.  The  other  is  split  on  one  side, 


END  VIEW  OF  KROM'S  FOURTH  IMPROVED  STEEL  CRUSHING  ROLLERS. 

Patented  July  16th,  1872,  and  patent  for  improvements  pending. 


so  that  when  the  heads  are  drawn  together  by  the  bolts, 
within  the  tires,  the  split  head  will  close  tightly  upon 
the  shaft. 


22 


Recapitulating  the  several  improvements  described 
we  have : 

1.  Steel  tires  and  the  method  of  securing  them. 

2.  Pulley-gearing. 

3.  Housing  to  inclose  the  rollers. 

4.  Swinging  pillow-blocks, 

5.  Bolts  to  take  the  crushing  strain. 

6.  The  hopper  for  spreading  the  ore. 

This  paper  would  not  be  complete  without  a  com- 
parison between  rolls  and  stamps  (other  pulverizing 
machines  not  being  worthy  of  attention  here).  On  this 
head  I  submit  the  following  observations : 

1.  The  capacity  of  any  machine  for  crushing  ore  is 
dependent  on  the  amount  of  crushing  surface  brought 
in  contact  with  the  ore  in  a  given  time,  and  the  effi- 
ciency with  which  the  crushing  surface  is  applied. 

2.  The  cost  of  crushing  depends  on  the  power  con- 
sumed and  the  expense  of  maintaining  the  machine  in  a 
working  condition. 

It  will  be  manifest  from  these  axioms  that  the 
employment  of  correct  mechanical  principles  with  sim- 
plicity of  construction  and  fewness  of  working  parts 
will  play  an  important  part  in  the  settlement  of  the 
question.  For  this  calculation  we  will  begin  by  com- 
puting the  capacity  of  two  sets  of  26-inch  rolls  with 
15-inch  face,  the  average  diameter  of  which  by  reason  of 
wear  will  be  say  24  inches.  One  pair  of  the  rolls  is  to 
receive  the  coarsely  crushed  ore  from  the  breakers,  and 
the  other  set  is  for  finishing  or  pulverizing.  Such  rolls, 
running  100  revolutions  per  minute,  will  bring  into 
contact  with  the  ore  113,100  square  inches,  and  the  two 
sets  of  rollers  are  therefore  equal  to  226,200  square 
inches  of  effective  crushing  surface  per  minute.  . 

The  usual  diameter  of  each  stamp-shoe  and  die  is  8 
inches,  and  the  area  is  therefore  50  square  inches  to 


23 


each  stamp.  Counting  all  this  as  effective  crushing  surface, 
we  have  for  each  stamp  (falling  say  90  drops  per  minute) 
4,500  square  inches  of  crushing  surface.  It  will  there- 
fore require  50  stamps  to  give  nearly  the  same  surface 
(namely  225,000  square  inches)  as  can  be  obtained  with 
two  sets  of  26-inch  rollers. 

Let  us  now  consider  the  two  machines  from  a  purely 
mechanical  point  of  view.  Stamps  crush  by  the  percus- 
sive effects  of  a  falling  weight,  and  the  power  consumed 
is  in  excess  of  the  work  performed,  because  it  takes  the 
same  power  to  operate  stamps,  whether  the  blows  are 
effective  or  not,  and  it  is  safe  to  assume  that  one-half 
the  power  is  lost.  With  rollers  the  crushing  force  is 
applied  continuously  in  one  direction,  and,  other  things 
being  equal,  it  must  be  evident  that  the  power  is  far 
more  economically  utilized.  Fig.  12  illustrates  the 
difference,  representing  the  faces  of  the  rolls  as  composed 
of  the  shoes  of  a  stamp  battery,  and  the  stamp-heads, 
stems  and  tappets  as  fastened  to  or  composing  the  fly- 
wheel, to  give  weight  and  steadiness  of  motion  and 
crushing  force  sufficient  to  overcome  irregularites  of 
resistance.  It  must  be  evident  that  if  the  rolls  (Fig  12) 
are  held  sufficiently  rigid  together,  the  pieces  of  rock 
falling  between  them  will  be  crushed  and  the  power 
consumed  will  be  in  proportion  to  the  work  done,  while 
the  surplus  power  will  be  stored  up  in  the  fly-wheel. 
If  the  same  amount  of  metal  were  put  in  stamps  on  the 
other  hand,  and  the  stamps  did  not  (as  of  course  they 
would  not)  give  in  falling  a  full  equivalent  of  useful 
work  for  the  power  consumed  in  raising  them,  the  ex- 
cess of  power  is  wasted  with  no  possibility  of  recovery. 
Moreover,  the  blow  of  a  stamp  has  no  regular  efficiency, 
and  is  always  only  partially  effective  by  reason  of  crush- 
ing on  too  much  ore  or  on  ore  already  fine  enough. 

With  rolls  the  crushing   effect  is  positive,   and  ore 


Fig.   12.    IDEAL  FIGURE  TO  ILLUSTRATE  RELATIVE  ECONOMY  OF  POWER  IN  STAMPS  AND  ROLLERS 


Fig.*  13.     THE  TOGGLE-LEVER  PRINCIPLE  COMPARED  WITH  FALLING  WEIGHTS. 


25 


cannot  pass  between  them  without  being  crushed  if 
they  are  properly  held  together.  Besides,  no  ore  which 
is  fine  enough  is  acted  upon  a  second  time.  Again,  the 
toggle-lever  principle  acting  in  rolls,  as  illustrated  in 
Fig.  13,  serves  to  give  the  necessary  crushing  pressure 
with  the  smallest  expenditure  of  power,  while  with 
stamps  the  contrary  is  the  case. 

1  have  met  persons  who  have  claimed  that  the  percus- 
sive effect  of  a  blow  has   some  quality  more  effective 
than   pressure.     Now   the    velocity   which  the  stamps 
attain  at  the  moment  of  striking  the   ore,  dropping  9 
inches,  is  7  feet  per  second,  while  the   surface  of  rolls 
24  inches  in  diameter,  running  100  revolutions  per  min- 
ute, travels  628  feet  per  minute,  or  about  10^  feet  per 
second.     This  gives  already  more  percussive  effect  than 
stamps ;  so  that,  if  percussion  is  any  aid  to  pulverizing, 
we  have  it  in   the  rolls  also  by  giving  them  velocity. 
But  I  do  not  adopt  this  reasoning.     The  whole  matter 
is  summed  up  in  the  statement,  that  stamps  must  attain 
a  certain  velocity  to  crush,  while  the  crushing  effect  of 
rolls  is  produced  at  either  high  or  low  velocity,  without 
material  change  in  quality  of  product ;  speed,  however, 
giving  increased  capacity. 

Simplicity  of  construction  has  also  been  claimed  for 
the  stamp-battery.  Let  us  see  if  this  claim  can  be 
sustained. 

The  working  or  wearing  parts  of  each  set  of  two  rolls, 
as  above  illustrated,  are  as  follows : 

4  journals  on  two  shafts. 

4  pillow-blocks  for  journals. 

2  crushing-rollers. 

2  side  wearing-plates. 

Total:  12  wearing-parts  to  each  set  of  rolls  or  24  in 
two  machines.  None  of  these  parts  can  break,  or  are 
subject  to  rapid  wear. 


26 


On  the  other  hand,  the  working  or  wearing  parts  in  a 
50-stamp  battery  are  : 

15  journals  on  5  shafts  (viz.,  10  stamps  on  each  shaft). 

5  cam-shafts. 

15  bearing-boxes  for  journals. 

50  stems. 

100  guide-boxes  for  stems. 

50  stamp-heads  (bosses). 

50  shoes. 

50  dies. 

50  cams  with  keys. 

50  tappets  with  keys. 

Total:  435  parts,  all  of  which  are  subject  to  severe 
wear  or  liable  to  break. 

Kecapitulating  our  comparison : 

1.  The  average   crushing  surface  of    26-inch  rolls  is 
226,200  square  inches,  while  the  crushing  surface  of  50 
stamps  is  only  225,000  square  inches  per  minute. 

2.  Two  sets  of  rolls  have  only  24  wearing  parts,  while 
a  50-stamp  battery  has  435  wearing  parts  (to  say  noth- 
ing about  the  screens  which  are  frequently  damaged, 
and  the  meshes  of  which  become  clogged  with  ore). 

3.  The  breakage  and  wear  of  stamps  are  much  greater 
than  that  of  rolls. 

4.  The  rotary  crushing  motion  of  rolls,  mechanically 
considered,  is  superior  and  more  economical  than  crush- 
ing under  falling  weight,  or  with  any  other  machine  or 
system. 

5.  By  the  toggle-lever  principle  in  rolls,  advantage  is 
taken  of  the  most  economical  and  powerful  means  of 
obtaining  the   necessary   crushing-pressure   on   the  ore, 
which  cannot  be  obtained  in  any  other  way,  and  is  not 
obtained  in  any  other  machine. 

Mr.  C.  A.  Stetefeldt,  in  an  appendix  to  his  able  paper 
on  RusseWs  Improved  Process  for  the  Lixiviation  of  Silver 


27 


Ores*  has  made  a  comparison  between  steel  rolls  and 
stamps,  which  I  here  reproduce. 

"COMPARISON    BETWEEN    KROM'S    ROLLS    AND    THE    STAMP- 
BATTERY. 

The  successful  introduction  of  Krom's  rolls  in  the  Bertrand 
lixiviation  mill,  Nevada,  is  of  such  importance  that  it  deserves 
notice  here.  In  comparing  stamps  and  rolls  we  have  to  consider  : 
1st.  The  physical  difference  of  the  pulp  produced.  2d.  The  ques- 
tion of  economy,  namely :  a.  In  regard  to  original  cost  of 
constructing  the  plant,  b.  The  wear  and  tear  of  each  machine, 
and  consumption  of  fuel. 

1.    The  Physical  Difference  of  the  Pulp  Produced. 

I  refer  here  to  the  well  known  fact,  that  if  pulp  produced  by 
rolls  or  by  stamps  is  sifted  through  the  same  size  of  screen,  the 
ore-particles  from  the  former  are  more  uniform  in  size,  and  contain 
much  less  impalpable  dust  than  those  from  the  latter.  It  has  been 
found  that  for  chloridizing-roasting  great  fineness  of  the  ore  is  en- 
tirely unnecessary — provided  the  silver  minerals  are  not  too  finely 
impregnated  in  the  gangue.  In  the  lixiviation  process  great  fineness 
of  the  ore  interferes  with  rapid  filtration.  From  this  it  follows 
that  ore  pulverized  by  rolls  is  in  the  most  favorable  condition  as 
far  as  the  mechanical  part  of  lixiviation  is  concerned. 

2.    The  Question  of  Economy. 

A  discussion  of  this  subject,  which  is  complete  and  thorough, 
and  compares  the  efficiency  of  rolls  and  stamps  under  varying 
conditions,  is  not  possible  at  present,  because  the  available  statistics 
concerning  Krom's  rolls  are  confined  to  those  from  the  Bertrand 
Mill.  Sufficient  evidence,  however,  has  accumulated  to  prove  the 
superiority  of  the  rolls  beyond  any  doubt.  Their  introduction  in 
the  Mt.  Cory  Mill,  Nevada,  will  soon  bring  additional  proof.  It 
seems  to  me  that  the  application  of  rolls  is  most  favorable  in  cases 
where  silver  is  extracted  by  lixiviation,  and  the  character  of  the 
ore  permits  comparatively  coarse  crushing  without  interfering 
with  good  roasting. 

A  comparison  between  rolls  and  stamps  will  be  made  from  the 
following  premises:  I  assume  that  the  crushing  capacity  of  two 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  vol.  xiii.,  p.  114. 


28 


:sets  of  Krom's  26-inch  rolls  is  equal  to  that  of  a  30-stamp  battery 
with  stamps  of  850  pounds,  dropping  from  7  inches  to  8  inches 
ninety-four  times  per  minute.  Mr.  Clark,  superintendent  of  the 
Bertrand  Mill,  states  that  he  can  crush,  with  two  sets  of  rolls,  100 
tons  of  ore  in  twenty-four  hours  to  such  a  fineness  that  all  will  pass 
through  a  No.  16  wire  screen,  consuming  not  over  4  cords  of  wood 
for  power.  The  ore  has  a  quartz  gangue,  and  is  by  no  means  an 
easy  crushing  ore.  The  fuel  required  for  running  30  stamps  is 
about  6  cords  of  wood  in  twenty-four  hours.  For  some  remote 
locality  in  the  West  the  following  prices  are  assumed,  namely: 
Freight  at  3  cents  per  pound;  lumber  at  $50  per  thousand  feet; 
wood  at  $6  per  cord;  wages  of  carpenters  at  $4.50,  and  of  mill- 
wrights at  $6.  Certain  items  of  construction  will  be  about  equal, 
namely:  conveyors,  elevators,  revolving  screens,  and  dust-cham- 
bers. Revolving  screens  are  also  used  in  connection  with  a  well- 
appointed  battery  in  order  to  separate  coarse  material  resulting 
from  the  breakage  of  battery-screens.  The  building,  however,  for 
rolls  will  be  much  smaller  than  that  for  the  battery,  and  a  saving 
of  not  less  than  $1,500  will  be  effected  in  its  construction.  Finally, 
the  rolls  requiring  less  power,  a  saving  of  at  least  $1,250  will  be 
made  in  providing  and  setting  up  engine  and  boilers  in  a  mill  with 
rolls 

Cost  of  Erecting  a  30-stamp  Battery. — The  plant,  including  hard 
wood  screen-frames  and  guides,  wooden  pulleys  on  cam-shafts, 
Tullock's  feeders  with  iron  hoppers,  and  all  necessary  bolts,  weights 
90,600  pounds,  and  costs  in  Chicago  *5,850,  according  to  a  state- 
ment of  Messrs.  Fraser  and  Chalmers.  The  framework  takes 
about  36,000  feet  of  lumber,  and  the  expense  of  setting  up  the 
battery  is  estimated  at  $4,000.  Hence,  total' cost  of  constructing  a 
30-stamp  battery  is: 


Plant  at  foundry,       ...... 
Freight,    
Lumber,             ....                   . 
Cost  of  setting  up,     . 

.     $5,850  00 
2,718  00 
1,800  00 
4,000  00 

To  this  has  to  be  added  in  order  to  compare  with  rolls  : 
Extra  cost  of  building,       
Extra  cost  of  engine  and  boilers, 

$14,368  00 

.       1,500  00 
.       1,250  00 

Cost  of  Erecting  two  sets  of  Krom's  r-6-inch  Rolls.—  The  amount 
•of  lumber  required  for  setting  up  the  rolls  alone  is  merely  nominal. 


29 


From  this  it  follows  that  also  the  labor  of  placing  the  rolls  must- 
be  trifling.     The  weight  of  one  set  of  26-inch  rolls  is  12,000  pounds,, 
and  the  cost  in  New  York  is  $2,250.     There  is  only  one  self-feeder 
required,  and  its  weight  is  estimated  at  2,000  pounds,  cost  $200. 
From  these  figures  we  deduce  the  following: 

Plant  at  foundry, $4,700  00 

Freight, 780  00 

Cost  of  setting  up,  including  lumber,         .         .         .          700  00 

Total,      . $6,180  00 

Difference  in  favor  of  rolls : 

$10,938  00* 


Wear  and  Tear  of  Stamps  and  Krorti's  Rolls. — In  comparing 
the  wear  and  tear  of  stamps  and  rolls  we  cannot  very  well  express 
it  per  ton  of  ore  crushed,  because  the  capacity  of  the  pulverizing 
machinery  is  a  function  of  the  hardness  of  the  ore,  and  of  the  fine- 
ness of  the  pulp  produced.  A  much  correcter  method  will  be  to 
take  the  figures  per  running  time  of  twenty -four  hours.  Making 
estimates  from  this  standpoint  it  is  supposed  that  the  wear  and 
tear  in  running  the  machinery  at  full  capacity  is  a  nearly  constant 
quantity,  while  the  capacity  is  variable  as  stated  above.  That  this 
assumption  is  correct  for  practical  purposes  has  become  evident 
to  me  by  a  comparison  of  the  battery  statistics  from  the  Manhattan 
and  Ontario  mills.  The  conditions  in  these  mills  are  by  no  means 
the  same.  There  is  a  difference  in  the  character  of  the  ore;  the 
Manhattan  uses  No.  50,  and  the  Ontario  No.  30  screens;  the  Man- 
hattan stamps  weigh  1,000  pounds,  those  at  the  Ontario  850 
pounds;  Ontario  stamps  drop  92  times  per  minute,  those  at  the 
Manhattan  about  100  times;  still,  in  comparing  the  wear  and  tear 
per  actual  horse-power  expended,  the  figures  are  very  nearly  the 
same.  Hence,  my  argument  does  not  lack  the  support  of  practical 
experience.  The  wear  of  rolls  is  principally  confined  to  the  steel 
tires,  that  of  the  battery  to  a  great  number  of  parts.  With  rolls 
the  steel  tires  can  be  consumed  to  within  less  than  one-half  inch  of 
their  thickness,  while  with  stamps,  the  shoes  and  dies  have  to  be 
exchanged  after  only  two-thirds,  or  less,  of  their  weight  has  been 
worn,  leaving  other  parts  out  of  consideration.  Another  point 
should  not  be  overlooked.  The  complicated  construction  of  the 
battery  causes  considerable  expense  in  skilled  labor  for  repairs, 
which,  in  the  case  of  rolls,  is  merely  nominal.  Advocates  of  the 

*In  both  estimates  elevators,  conveyors,  and  revolving  screens  are  not  included,  as  stated  previously. 


30 


battery  have  argued  that  its  great  advantage  is  the  continuance  of 
its  operation  if  one  battery  of  five  stamps  gets  out  of  order,  while 
both  sets,  or  three  sets  of  rolls,  as  the  case  may  be,  have  to  be 
stopped  if  repairs  are  needed  for  one  set.  But  it  is  just  the  solid 
construction  of  Krom's  rolls  which  reduces  stoppages  from  this 
cause  to  a  minimum.  The  system  of  elevators,  screens,  hoppers 
and  conveyors,  if  properly  constructed,  will  get  out  of  order  very 
rarely.  How  often  it  is  necessary  to  hang  up  stamps  for  repairs  is 
too  well  known  to  require  any  statistical  proof. 

Wear  and  Tear  of  Ifrom's  Rolls. — As  to  statistics  of  wear  and 
tear  of  Krom's  rolls  I  am  confined,  at  present,  to  those  from  the 
Bertrand  Mill.  Mr.  R.  D.  Clark  states  that  two  sets  of  steel  tires 
•  crushed  in  round  figures  20,000  tons  of  ore. 

As  stated  previously,  the  full  capacity  of  the  rolls  is,  in  twenty- 
four  hours,  100  tons,  the  ore  being  sifted  through  a  No.  16  screen. 
In  the  beginning,  however,  the  ore  was  crushed  much  finer,  name- 
ly, so  as  to  pass  a  No.  20  screen,  and  the  daily  capacity  of  the  rolls 
was  much  less.  Taking  this  into  consideration,  the  actual  wear- 
ing capacity  of  the  tires  cannot  be  estimated  at  less  than  250  work- 
ing days.  The  cost  of  this  wear  is  as  follows: 

Two  sets  of  steel  tires  at  New  York,         .         .         .          $764  00 
Freight  on  3,264  pounds,  at  3  cents,         ...  98  00 

Total, $862  00 

Wear  and  tear  per  twenty-four  hours : 

In  steel  tires,            .......  3  45 

In  other  parts,  screens,  supplies  and  lubricants,        .  1  75* 

Wages  for  repairs, 1  25* 


Total,  $6  45 

Wear  and  Tear  of  Stamps. — I  have  been  favored  with  correct 
.statistics  from  three  of  the  most  prominent  mills  in  the  West, 
namely:  the  Manhattan,  Nevada;  the  Ontario,  Utah;  the  Lexing- 
ton, Montana.  Taking  into  consideration  the  somewhat  abnormal 
conditions  at  the  Manhattan  Mill,  in  so  far  as  the  weight  of 
stamps  there  is  1,000  pounds,  and  the  number  of  drops  is  greater 
than  in  either  of  the  other  mills,  causing  a  more  frequent  breakage 
of  stems  and  cam-shafts;  further,  that  the  statistics  from  the 
Lexington  Mill  are  those  from  the  first  year's  run,  where  certain 
breakages  are  reduced  to  a  minimum;  finally,  that  freight  in  these 

*These  figures  will,  no  doubt,  be  considered  too  high  by  Mr.  Krom  and  Mr.  Clark.    I  consider  it 
;  safe,  however,  to  provide  a  limit  for  accidents. 


31 


localities,  on  account  of  direct  railroad  communications,  is  slightly 
less  than  I  have  assumed  in  my  premises,  I  arrive,  by  making  such 
allowances,  at  the  following  figures  for  wear  and  tear  of  a  30-stamp 
battery  per  twenty-four  hours  running  time: 

In  all  parts  subjected  to  wear  and  breakage,   supplies, 

screens,  and  lubricants,* $11  50 

Wages  for  repairs, 5  50 


Total, •     $17  00 

Wear  and  tear  of  rolls,        • 6  45 


Difference  in  favor  of  rolls,    .         .         .         .         .  $10  55 

Interest  and  Amortisation. — In  comparing  the  expense  of  run- 
ning rolls  and  stamps,  interest  and  amortisation  on  the  excess  of 
capital  required  in  the  original  construction  of  the  plant  for  stamps 
cannot  be  neglected.  Considering  the  short  life  of  most  silver 
mines  in  this  country,  this  item  should  not  be  taken  at  a  lower  rate 
than  15  per  cent,  per  annum.  If  we  take  the  running  time  of  a 
mill  at  three  hundred  and  fifty  days  in  the  year,  and  consider  that 
a  mill  with  stamps  will  cost  $10,938  more  than  one  with  rolls,  the 
interest  and  amortisation  amount  to  $4.68  per  day. 

Summary. — From  the  above  we  find  the  following  daily  saving 
in  a  mill  with  two  sets  of  Krom's  26-inch  rolls  as  compared  with 
30  stamps: 

Wear  and  tear,  and  repairs, $10  55 

Interest  and  amortisation, 4  68 

Fuel,  2  cords  of  wood,  at  $6, 12  00 


Total $27  23 

If  no  great  accuracy  can  be  claimed  for  this  estimate,  it  is  the 
best  which  can  be  given  at  present. 

Mr.  Krom,  supported  by  Mr.  Clark,  claims  that  two  sets  of  rolls 
will  crush  more  ore  than  30  stamps.  Others  will  consider  my 
estimate  too  much  in  favor  of  the  rolls.  Time  will  establish  the 
correctness  or  fallacy  of  these  views." 

*0f  this  amount,  the  wear  and  tear  of  shoes  and  dies  represents  only  40  per  cent.;  tappets,  bosses, 
cams,  stems,  cam-shafts,  flanges,  and  boxes,  33  per  cent.;  and  screens,  lubricants,  screen-frames,  bat- 
tery guides,  and  carpenters'  and  machinists'  supplies,  22  per  cent. 


32 


To  the  comparison  of  Mr.  Stetefeldt  I  need  add 
nothing  except  to  corroborate  and  emphasize  it  from 
later  data  of  experience. 

Since  Mr.  Stetefeldt's  paper  was  written,  the  capacity 
of  the  rolls  in  the  Bertrand  mill  has  been  rated  at  150 
tons  per  twenty-four  hours  crushing  to  pass  a  16-mesh 
screen.  This  is  50  per  cent,  more  than  Mr.  Stetefeldt 
felt  justified  in  assuming.  The  rolls  have  also  been  put 
in  successful  operation  in  the  Mt.  Cory  mill,  Nevada, 
and  the  Haile  mill,  South  Carolina. 

What  the  full  capacity  of  the  improved  rolls  is,  has 
not  yet  been  demonstrated  by  actual  test,  as  either  the 
screening  or  elevator  capacity  has  not  been  sufficient  to 
allow  a  complete  demonstration  of  this  point.  We  only 
know  that  at  the  Bertrand  mill  the  rolls  crushed  50  tons 
of  hard  ore  in  twelve  hours,  and  in  the  Mt.  Cory  mill, 
50  tons  to  30-mesh  fineness  in  the  same  time.  If  we 
rate  the  capacity  of  stamps  of  850  pounds  at  2  tons  per 
stamp  in  twenty-four  hours,  doing  the  same  kind  of 
work,  this  would  show  that  two  sets  of  26-inch  rolls  are 
equal  to  50  stamps.  The  calculation  given  in  the  pre- 
ceding pages,  and  results  in  practice  justify,  I  think,  this 
rating. 

Mr.  Clark,  of  the  Bertrand  Company,  says  :  "  We  have 
demonstrated  the  following  facts  :  That  we  can  pulp 
more  ore  with  the  rollers  than  can  be  done  with  a 
40-stamp  battery;  that  we  have  crushed  9,000  tons  of 
ore  without  a  dollar's  expense  in  repairs;  that  we  have 
done  it  with  less  than  one-half  the  power  that  would 
have  been  required  had  we  used  stamps ;  that  the  cost 
of  repairs,  wear  and  tear,  will  not  exceed  one-quarter  of 
that  of  crushing  with  stamps ;  that  we  make  less  dust, 
jar  and  noise." 

At  a  later  date  Mr.  Clark  says  :  "  We  crushed  15,000 
tons  of  ore  before  putting  new  tires  on  the  fine-crushing 


33 


rollers,  and  have  crushed  now  20,000  tons ;  and  it  will 
be  two  or  three  months  yet  before  we  will  put  new  tires 
on  the  coarse-crushing  rollers.  It  will  be  safe  to  calcu- 
late that  each  set  of  tires  with  a  set  of  composition 
liners  for  journals  will  last  to  crush  20,000  tons  of  ore. 
There  has  been  no  other  expense  for  repairs  upon  our 
rollers  except  the  check-pieces." 

On  the  above  basis  (crushing  20,000  tons  with  a 
wear  of  two  sets  of  steel  tires  and  one  set  of  composi- 
tion liners)  the  cost  of  renewal  at  present  prices  of  steel 
will  be  as  follows  : 

Two  sets  of  steel  tires, $530  00 

Freight  on  3,264  pounds,  at  3  cents,  .         .         .  98  00 

Composition  liners  for  journals  and  check-piece,       100  00 

Total $728  00 

which  amounts  to  3T6¥  cents  per  ton  of  ore. 

But  after  all  that  has  been  proved  for  rolls  it  is  still 
sometimes  asserted  that  they  are  only  suitable  for  coarse 
crushing;  that  ore*  cannot  be  pulverized  with  them 
sufficiently  fine  for  amalgamation  and  other  purposes 
where  pulverizing  is  needed,  such  as  cement,  phosphate- 
rock,  etc.  This  is  true,  as  before  pointed  out,  of  ordin- 
ary cheap  rollers  only.  The  same  assertion  was  made 
when  it  was  proposed  to  adopt  rolls  in  the  Bertrand 
mill  for  pulverizing  ore  for  lixiviation ;  and  almost 
everybody  who  knew  of  the  affair  predicted  that  the 
rolls  would  prove  a  failure.  At  the  same  time,  such 
critics  admit  that  stamp-batteries,  centrifugal  roller-mills, 
attrition-mills,  ball-pulverizers,  mill-stones,  and  various 
impracticable  machines  will  pulverize.  It  would  be  as 
good  reasoning  to  argue  that  a  heavy  load  can  be  drawn 
on  a  sleigh  on  bare  ground,  but  that  the  same  heavy 
load  cannot  be  carried  on  a  strong  and  well-constructed 
wagon  or  railroad  car.  Crushing  with  rolls  is  carrying 


34 


the  load  on  wheels  while  all  the  other  devices  are  similar  to 
dragging  the  load  with  great  loss  of  energy. 

Rolls  as  a  pulverizing  machine,  if  properly  con- 
structed, cannot  be  improved  upon  either  in  principle 
of  operation  or  in  economy  of  results.  All  the  parts 
are  of  such  a  character  as  to  contribute  to  their  dura- 
bility, and  there  is  no  limit  to  proportioning  the  journals 
so  as  to  fit  them  to  carry  any  load  that  may  be  put  upon 
them.  The  capacity  of  rolls  for  quantity  and  hard  work 
is  far  greater  than  that  of  any  other  existing  device. 

Rolls  are  at  last  receiving  the  recognition  they  de- 
serve as  a  pulverizing  machine.  It  is  now  proposed  to 
employ  rolls  to  crush  fine  after  the  ore  has  passed  the 
stamp-battery,  so  as  to  increase  the  capacity  of  an  exist- 
ing plant — which  is  a  complete  reversal  of  all  former 
ideas  on  the  subject.  Yet  I  have  sold  rolls  for  this 
purpose.  Considering  the  subject  from  a  mechanical 
standpoint  it  is  astonishing  that  rolls  were  not  brought 
to  perfection  and  widely  adopted  long  ago. 


35 


KROM'S    SYSTEM    OF    PNEUMATIC    CONCEN- 
TRATION  OF   ORES. 

Concentration  of  ores  by  means  of  air  is  a  problem 
which  has  received  much  study,  and  has  been  the  sub- 
ject of  many  experiments,  both  in  this  country  and  in 
Europe.  The  employment  of  air  for  the  separation  of 
ores  was  generally  admitted  to  be  a  matter  of  consider- 
able importance,  but  soon  after  I  had  shown  that  air 
could  be  employed  successfully  as  the  concentrating 
agent,  and,  in  fact,  had  demonstrated  its  superiority, 
then  some  critics  claiming  to  be  conversant  with  the 
theory  and  art  of  ore  dressing  began  to  write  treatises 
to  prove  the  impracticability  of  employing  air  for  this 
purpose  ;  they  said  air  is  "  specifically  too  light,  and 
could  move  only  small  particles."  These  critics  evi- 
dently had  not  heard  of  a  cyclone,  or  the  various  appli- 
cations of  air  as  a  motive  power.  In  my  experience  I 
found  that  air  applied  in  intermittent  impulses,  similar 
to  water  in  the  wet-jig,  exhibited  phenomena  favorable 
to  its  employment  as  a  concentrating  medium.  The 
theory  found  in  literature,  and  relied  upon  by  the  sev- 
eral writers  to  sustain  their  criticisms,  was  that  for 
separating  two  particles  of  solids  of  different  density, 
such  liquid  medium  is  the  most  effective  that  possesses 
a  density  lower  than  the  density  of  the  specifically 
heavier  particles,  and  higher  than  the  specifically  lighter 
ones.  For  example  (they  said),  let  us  suppose  that  an 
ore  consisting  of  galena,  specific  gravity  7.5  and  quartz, 
specific  gravity  2.5,  so  finely  crushed  that  each  particle 
will  consist  of  either  galena  or  gangue  to  be  placed  in  a 
liquid  of  a  specific  gravity  of  5,  then  it  is  evident  that 
the  quartz  would  remain  floating  on  the  surface,  while 
the  galena  would  sink  to  the  bottom." 


36 


A  medium  of  intermediate  density  is  not  only  imprac- 
ticable to  obtain,  but  would  not  serve  as  the  concentrat- 
ing medium  if  we  had  it.  To  separate  minerals  of  different 
specific  gravity,  a  medium  of  lower  density  is  required 
with  sufficient  motion  imparted  to  it  to  give  the  neces- 
sary resistance. 

The  less  dense  between  certain  limits  that  medium  is 
the  better  it  will  serve  the  purpose.  In  the  wet  and 
dry  jig  it  is  the  resistance  caused  by  the  motion  of  the 
fluid  that  effects  the  separation.  In  practice  we  can 
only  use  one  of  two  mediums,  air  or  water,  all  others 
being  chimerical.  0 

A  mathematicMliscussion  of  the  subject  would  no 
doubt  point  out  a  theoretical  medium  of  such  density 
that  its  effect  taking  power,  adhesion,  etc.,  into  consid- 
eration would  be  a  maximum,  and  that  air,  instead  of 
water,  would  be  found  to  be  nearest  to  that  theoretical 
medium.  In  technical  literature  it  is  stated  uThat  the 
difference  between  diameters  of  spheres  obtaining  equal 
speed  falling  in  air  is  less  than  between  diameters  of 
spheres  falling  equally  fast  in  water."  That  is,  a 
-J-"  globule  of  galena  and  |-"  globule  of  quartz  fall  with 
equal  speed  in  still  and  moving  water.  But  it  is  asserted 
that  in  air  the  -f-"  globule  of  quartz  would  fall  much 
faster.  This,  however,  applies  to  air  at  rest,  which 
would  not  comply  with  the  conditions  in  practice  which 
requires  the  air  to  have  a  motion  sufficient  to  make  its 
resistance  equal  to  water.  It  is  a  remarkable  circum- 
stance that  none  of  these  theoretical  writers  have  com- 
prehended the  following  facts : 

1st.  That  either  air  or  water  can  be  converted  into 
the  exact  "  theoretical  and  ideal  minimum  "  by  giving 
motion  to  it  to  produce  any  degree  of  resistance. 

2d.  That  the  principle  of  uniform  intermediate  resist- 
ance does  not  succeed  in  practice,  but  that  our  most 


37 


successful  practice  is  based  on  the  intermittent  resistance 
of  the  concentrating  agent. 

To  prove  the  incorrectness  of  the  formulas  on  the 
subject  of  the  free  fall  of  mineral  grains  in  air  and  water 
as  applied  to  ore  dressing,  I  erected  two  glass  tubes  (as 
illustrated)  each  2"  in  diameter  and  8'  long.  One  of 
these  tubes  I  filled  with  water  and  through  the  other 
I  forced  a  current  of  air.  I  found  that  practically  as 
stated  the  -J-"  globule  of  galena  and  |"  globule  of  quartz 
are  equal  falling  in  a  column  of  water,  but  in  a  current 
of  air  adjusted  to  retard  the  galena  from  falling  to  the 
same  extent  as  in  water,  the  |-"  globule  of  quartz  was 
sustained  and  did  not  fall,  but  oscillated  in  the  open 
end  of  the  tube. 

I  also  employed  bodies  of  other  forms  with  conical 
heads  (as  illustrated  in  the  cut).  In  experimenting 
with  these  I  regulated  the  current  of  air  in  the  air  tube 
to  give  the  same  resistance  as  water  would  to  the  falling 
bodies  of  equal  weight  and  size,  one  in  the  water,  and 
the  other  in  the  current  of  air,  both  reaching  the  bottom 
in  equal  time.  I  then  let  fall  Nos.  1  and  3  in  water, 
and  when  No.  1  reached  the  bottom,  No.  3  was  about 
10  behind.  Next  I  let  fall  the  same  Nos  1  and  3  in 
the  current  of  air,  and  No.  1  fell  in  the  same  time  in 
the  air  current  as  it  did  in  water,  but  No.  3  did  not  fall, 
but,  like  the  quartz  ball,  it  oscillated  in  the  open  end  of 
the  tube.  Philosophical  reasoning  would  have  led  to 
no  other  conclusion  than  that  the  galena  and  quartz 
globules  would  fall  with  equal  velocity  in  the  air  cur- 
rent, under  the  conditions  here  described.  The  experi- 
ment, however,  demonstrated,  as  practice  had  before,  the 
superiority  of  air  as  the  concentrating  medium.  This 
experiment  has  been  criticised  in  a  paper  written  by 
J.  C.  Bartlett,  A.  M.  Mr.  Bartlett  claims  that  the 
more  favorable  effect  was  due  to  the  narrow  cross 


Wote-r 


ILLUSTRATING  EXPERIMENTS  WITH  EQUAL  FALLING  GRAINS 
IN  WATER  AND  AIR. 


I/ 


Wle 


ILLUSTRATING  EXPERIMENTS  WITH  EQUAL  FALLING  GRAINS 
IN  WATER  AND  AIR. 


40 


section  of  the  tubes.  To  avoid  such  criticisms  I  per- 
formed the  second  part  of  the  experiment  with  the 
conical  headed  tacks.  In  this  experiment  the  proper 
conditions  as  required  by  Mr.  Bartlett  were  perfectly 
complied  with,  but  Mr.  Bartlett,  however,  ignored  this 
part  of  the  experiment.  On  these  criticisms  the  dis- 
tinguished Councilor  Althaus,  one  of  the  Centennial 
judges,  says:  "It  must  not  be  overlooked  that  in 
pneumatic  jigging  the  grains  suspended  in  the  stream  of 
air  are  always  in  narrow  air  spaces,  and  that  in  cases  of 
the  large  grains  in  comparison  with  the  adjacent  smaller, 
but  specifically  heavy  ones,  they  are  similarly  situated 
to  those  in  Krom's  experiment  in  narrow  glass  tubes. 
In  the  opinion  of  the  author,  therefore,  practical  ex- 
perience alone  can  decide  which  process,  the  hydraulic 
or  pneumatic,  can  effect  the  closer  separation  according 
to  specific  gravity  and  size  of  grain."  These  remarks  of 
the  councilor  are  a  complete  answer  to  every  criticism 
made  against  the  pneumatic  system  of  concentration. 


ENDORSEMENTS  OF  PNEUMATIC  CONCEN- 
TRATION. 

Dr.  R.  W.  Raymond  in  the  Engineer  and  Mining 
Journal,  Dec.  21,  1878,  in  reviewing  a  treatise  on  the 
subject  of  ore  dressing  by  E.  F.  Althaus,  member  of  the 
Royal  Mining  Court,  Breslau,  Germany,  and  judge  of 
group  1,  Centennial  Exhibition,  says:  " Councilor 
Althaus,  fortunately  for  the  profession,  represented 
group  1  at  the  Centennial  Exhibition,  a  member  of  the 
jury  of  that  group,  and  by  another  piece  of  good  luck  or 
judgment  the  subject  of  ore  dressing  was  assigned  to 
him.  The  treatise  on  that  subject  which  he  contributes 
to  the  Reports  and  Awards  is  a  model  of  intelligent 


41 


criticism,  and  even  as  a  manual  of  art  superior  to  any- 
thing we  possessed  in  the  English  language  before  its 
appearance." 

The   following   is    taken    from    Councilor   Althaus' 
Centennial  report  on  ore  dressing: 


"THE  PKINCIPLES  OF  KKOM'S  PNEUMATIC 
JIGGING."* 

uThe  idea  of  using  air  as  the  medium  for  the  sep- 
aration of  mineral  grains,  rejected  in  Europe  as  fruit- 
less, was  again  taken  up  in  an  entirely  new  direction  in 
the  United  States  by  Stephen  R.  Krom  of  New  York, 
in  the  year  1868,  and  has  since  been  systematically 
developed  in  exceedingly  ingenious  machines,  which 
were  an  ornament  to  the  ^Centennial  Exhibition.  This 
new  treatment,  only  within  a  few  years  successfully 
introduced  into  some  ore  dressing  establishments,  is  yet 
too  little  known  in  its  economical  results  to  give  a  final 
judgment  on  its  possible  advantage  over  ore  dressing  in 
the  wet  way,  but  it  can  even  now  be  designated  as  a 
surprising  advance  in  the  art  of  ore  dressing.  That  the 
spirit  of  invention  even  in  this  department  has  so  decided- 
ly succeeded  in  producing  unheard  of  mechanical  effects, 
in  contradiction  to  prevailing  theoretical  opinions,  and 
furnishing  an  ocular  demonstration  so  clear  that  the 
correctness  of  the  facts  cannot  be  disputed. 

The  earlier  experiments  of  air  separation  were  con- 
fined to  a  continuous  stream  of  air  produced  by  a  ven- 
tilator, in  a  high,  horizontal  and  narrow  conductor  (two  or 
three  metres  square)  through  which  the  dried  mineral 
grains  introduced  from  above  were  separated  in  a  manner 

*  The  autht  r  had  an  opportunity  at  the  Centennial  Exhibition  of  observing  a  Krom  machine 
at  work. 


42 


entirely  similar  to  that  of  the  horizontal  stream  of 
water,  working  in  the  settling  pit  according  to  the 
principle  of  free  fall.  But  Krom  starts  with  the  funda- 
mental idea  of  compressing  the  air  by  means  of  a  kind 
of  piston  with  quick  successive  strokes,  and  thus  com- 
pressed to  let  it  work  with  great  rapidity  through  a  low 
stratum  of  mineral  grains,  previously  assorted  according 
to  size  (sized),  which  rests  on  fine  sieves  enclosed  lat- 
erally in  a  narrow  space.  Krom's  pneumatic  jig  or  dry 
concentrator  is  similar  to  the  continuous  hydraulic  jig  in 
outward  appearance,  and  must  be  designated  as  an 
intermittent  working  air  stream  apparatus,  in  which, 
therefore,  the  dynamic  effect  of  the  living  force  produced 
by  an  upward  jerk  through  the  dense  medium  has  a 
more  energetic  effect  than  by  free  fall.  In  the  employ- 
ment of  air  in  puffs  as  a  medium,  its  inferior  density  is 
a  decided  advantage.  With  water  the  vis  inertia  of  the 
mass  of  the  medium  to  be  moved  prevents  driving  a 
jigger  at  more  than  60  to  120  strokes  per  minute. 
Troublesome  setting  back  of  the  water  takes  place, 
which  acts  detrimental  to  the  separation  on  the  sieve, 
to  avoid  which  either  the  stroke  and  velocity  must  be 
diminished,  or  a  complicated  arrangement  be  made  use 
of.  On  the  contrary,  the  air  escapes  at  each  stroke 
without  set  back,  and  it  is  therefore  possible  to  drive 
the  pneumatic  jigger  420  to  500  strokes  per  minute, 
consequently  very  much  more  rapidly  than  the  hydraulic 
one. 

Air  is  a  medium  to  be  obtained  every  where,  while  the 
procuring  of  the  necessary  water  supply  is  attended  with 
difficulty  as  a  rule,  and  in  many  places  is  impossible. 
While  the  grains  to  be  separated  have  to  pass  over  a 
distance  of  one  or  two  metres  on  the  continuous 
hydraulic  jigger,  they  have  to  pass  over  only  thirteen 
centimetres  of  sieve  length  on  Krom's  machine.  This 


43 


apparatus  can,  therefore,  for  the  sake  of  concentrated 
efficiency,  be  more  extended  laterally  without  assuming 
troublesome  proportions.  As  the  adhesive  effect  of  air 
compared  with  water  is  extremely  small,  it  is  evident 
that  sands  can  be  treated  pneumatically  which  are  very 
much  finer  than  the  finest  treated  on  the  hydraulic 
jigger.  The  dry  sand  forms  a  loose  mass  easily  pene- 
trated by  the  compressed  air,  while  on  the  hydraulic 
jigger  it  is  raised  altogether  in  a  closely  adhering  mass 
by  the  water,  thrust,  and  even  in  falling  hinders  its  own 
separation  through  mutual  adhesion.  While  grains 
from  .5  to  1  millimetre  can  scarcely  be  prepared  on  the 
hydraulic  jigger,  it  is  said  that  grains  of  .01  millimetre 
can  be  separated  pneumatically." 

Prof.  Alex.  Trippel,  at  the  close  of  an  article  on  ore 
dressing  published  in  the  Mining  Record,  June  25,  '83, 
says:  "  We  will  probably  never  have  dressing  works 
which  will  save  all  that  is  valuable,  and  work  without 
any  disadvantage,  but  taking  all  points  into  con- 
sideration, I  think  that  the  pneumatic  principle  as 
applied  by  Mr.  Krom  will  gradually  be  more  appre- 
ciated as  one  which  is  the  least  wasteful." 

T.  Gr.  Negus,  Esq.,  the  former  superintendent  of  the 
Clear  Creek  Co,  Col.,  says: 

"  There  is  a  very  great  difference  in  the  quality  of  ore 
for  concentrating.  Some  ores  are  susceptible  of  very 
close  concentration,  while  others  are  not ;  for  instance, 
some  ores  contain  precious  metals  in  the  gangue  in  such 
fine  particles  that  disintegration  by  crushing  is  impos- 
sible. In  such  ores  a  high  percentage  cannot  always  be 
obtained.  I  am  prepared  to  say,  however,  that  the 
Krom  system  of  dry  concentration  is  eminently  superior 
to  all  others  of  which  I  have  any  knowledge  for  all 
grades  of  ore." 

Mr.  Stetefeldt  in  his  recommendations  of  May  4th, 


44 


1883,  to  the  Alta  Montana  Co.,  says:  "In  examining 
the  advantages  of  the  Krom  system  of  dry  concentration 
compared  with  the  wet  method,  we  find,  1st.  That 
Krom's  air  jig  effects  a  more  complete  separation  of 
minerals  of  different  specific  gravities  than  the  water  jig. 

2d.  That  material  of  greater  fineness  can  be  treated 
in  the  air  jig  than  in  the  water  jig. 

3d.  That  in  wet  concentration  the  great  losses  occur 
in  those  machines  which  treat  material  too  fine  for  the 

jig- 

4th.  That  the  dust  which  results  in  the  Krom  system 

is  of  higher  value  than  the  original  ore,  and  is  a  concen- 
trated product.  But  besides  this  other  conditions  are 
to  be  considered.  If  the  products  of  concentration  are 
to  be  roasted  and  a  portion  of  them  have  previously  to 
be  finer  pulverized,  it  becomes  necessary  to  get  them 
perfectly  dry.  Now  it  is  evident  that  it  must  be  very 
much  cheaper,  and  require  a  much  simpler,  and  less 
bulky  plant  to  dry  the  ore  after  it  leaves  the  crusher 
than  to  remove  the  moisture  from  concentrations  and 
slimes  completely  saturated  with  water.  It  furnishes 
dry  dust  ready  for  the  roasting  furnace,  concentrations 
ready  for  finer  pulverization,  .a  concentrated  product 
ready  for  smelting,  purer  and  of  higher  percentage  in  lead 
than  the  water  jigs.  It  also  makes  possible  a  better 
arrangement  of  the  location  of  the  dry  kiln  in  connec- 
tion with  the  mill." 

Pneumatic  concentration  has  not  so  far  had  an  oppor- 
tunity for  a  long  and  fair  trial ;  when  it  does  you  will 
see  as  convincing  a  demonstration  favorable  to  air  as  the 
concentrating  medium,  as  has  been  shown  in  favor  of 
employing  rollers  in  place  of  stamps.  By  this  I  do  not 
mean  to  say  that  pneumatic  concentration  has  not  made 
a  good  record,  on  the  contrary,  it  has  shown  its  superi- 
ority whenever  and  wherever  tested.  In  the  Clear 


45 


Creek  Company's  Mill  at  Georgetown,  Colorado,  the 
pneumatic  jigs  gave  10  to  15  per  cent,  better  results 
than  tests  on  the  same  ore  in  competition  with  wet  con- 
centration. This  mill  was  kept  in  operation  as  long  as 
ore  could  be  obtained.  At  Galena,  Nevada,  in  the 
White  &  Shiloh  Mining  Company's  Mill  it  gave  results 
satisfactory  to  the  owners,  and  above  the  guaranteed 
percentage  of  saving,  and  on  such  ore  which  previous 
trials  had  shown  could  not  be  successfully  separated  by 
the  wet  process,  and  this  works  remained  in  successful 
operation  until  the  mine  produced'no  more  ore. 

At  Austin,  Nevada,  the  results  were  decidedly  in 
favor  of  pneumatic  concentration.  At  Wickes,  Montana, 
the  dry  concentration  works  were  destroyed  by  fire 
before  they  had  been  put  in  proper  running  order,  or 
placed  in  charge  of  persons  competent  to  run  them. 

Also  the  works  at  Star  Canyon,  Nevada.  The  first 
mill  erected  on  the  pneumatic  system  have  always 
been  considered  a  success.  It  is  purely  prejudice  and 
the  misinterpretation  of  the  theories  applicable  to  ore 
dressing  and  accidental  circumstances  which  has  prevented 
the  more  rapid  introduction  of  the  pneumatic  system. 


46 


THE  PNEUMATIC  JIG. 

The  first  plate,  Fig.  1,  is  a  perspective  view  of  the 
pneumatic  jig.  Fig.  2  is  an  end  view,  and  Fig.  3  a 
transverse  sectional  view.  The  machine  is  composed 
essentially  of  the  following  parts:  A  receiver,  H,  to 
hold  the  crushed  ore ;  and  ore  bed,  O,  on  which  the  ore 
is  submitted  to  the  actions  of  the  air;  the  two  gates, 
G,  G,  one  to  regulate  the  flow  of  ore  from  the  receiver 
H,  the  other  to  determine  the  depth  of  ore  on  the  ore  bed ; 
passage  C,  in  which  the  concentrated  ore  descends,  and 
roller  R,  to  effect  and  regulate  the  discharge  of  the  same ; 
a  fan,  B,  to  give  the  puffs  of  air,  a  trip- wheel  T,  lever 
L,  and  spring  S,  to  operate  the  fan,  and  a  ratchet-wheel 
W,  and  pawl  P,  to  impart  revolution  to  the  roller  R. 

The  mode  of  operating  the  machine  is  as  follows: 
Ore  is  placed  in  the  receiver  H,  and  the  driving  pulley 
set  in  motion.  The  cam  shaped  trip- wheel  T,  fixed  on 
the  opposite  end  of  the  pulley-shafts,  works  against  the 
lever  L.  By  the  alternate  action  of  this  wheel,  forcing 
the  lever  in  one  direction,  and  the  spring  which  suddenly 
carries  it  back  again,  the  fan  B  is  made  to  swing  on  the 
shaft  I,  sending  at  each  upward  movement  a  quick  and 
sharp  puff  of  air  through  the  ore  bed,  and  lifting  slightly 
the  ore  lying  on  it.  There  are  six  projections  upon  the 
trip- wheel,  so  that  the  moderate  speed  of  80  to  90 
revolutions  per  minute  will  give  480  to  540  upward 
movements  of  the  fan  in  the  same  time,  and  a  correspond- 
ing number  of  puffs  of  air  to  agitate  the  ore.  This  rate 
is  sufficient  to  secure  a  steady  motion  of  the  heavy  pulley, 
and  yet  not  so  fast  as  to  produce  any  perceptible  vibration, 
the  machine  working  smoothly  and  easily.  The  ore  bed 
is  composed  of  wire-gauze  tubes,  placed  at  distances 
from  each  other  of  T3¥,  1,  f  and  -J-  of  an  inch,  accord- 
ing to  the  grade  of  ore  to  be  concentrated,  the  finer 


47 


Patented  Aug.  4,  1SC8,  and  Sept.  1, 1868  ;  Ke-issue  Nov.  3,  1868;  Re-issue  June  20,  1871 ;  Patented 
Dec.  5,  1871,  and  Patents  pending  for  improvements. 


48 


requiring  the  tubes  set  nearer  together,  while  the  coarser 
allow  the  tubes  to  be  placed  farther  apart.  The  ore  bed 
(situated  in  front  of  the  fan,  as  plainly  shown  in  the 
sectional  view)  is  composed  of  these  tubes.  Their  ends 
next  to  the  fan  being  open,  the  air  from  the  bellows 
enters  and  escapes  through  the  top  and  sides  of  the  tubes, 
agitating  the  ore  that  lies  on  them,  and  also  that  between 
them  near  the  surface. 

The  ore  between  the  tubes  rests  on  that  immediately 
underneath  in  the  passage  C,  and  sinks  as  fast  as  the 
roller  K  effects  its  discharge.  The  tubes  being  open  also 
on  the  bottom,  any  fine  ore  passing  through  the  meshes 
of  the  wire  gauze  descends  with  the  main  body  C,  thus 
preventing  any  liability  of  the  tubes  to  fill  up  with  fine 
ore. 

The  roller  R  is  operated  (as  above  mentioned)  by 
means  of  the  ratchet-wheel  W  and  pawl  P,  and  the  latter 
being  carried  by  a  crank  on  the  trip- wheel,  it  follows 
that  its  speed  is  governed  by  the  speed  of  this  wheel, 
which  also  gives  motion  to  the  fan  B.  By  this  connection 
the  fan,  which  effects  the  concentration,  and  the  roller, 
which  discharges  the  concentrated  ore,  are  made  to  act 
in  concert  with  each  other.  The  importance  of  this 
feature  will  be  apparent  when  it  is  remembered  that  the 
amount  of  ore  concentrated  in  a  given  time  depends  on 
the  rapidity  of  the  puffs  of  air,  so  that  the  motion  of  the 
discharge  roller  R  should  be  regulated  to  correspond 
with  the  speed  of  the  fan. 

The  crank  which  carries  the  pawl  can  also  be  varied 
in  length  so  that  the  speed  of  the  rollers  may  be  regulated 
according  to  the  richness  of  the  ore.  As  already  stated, 
the  upper  gate,  G,  governs  the  flow  of  ore  from  the  re- 
ceiver, H,  to  the  ore  bed,  while  the  lower  gate,  G,  regulates 
the  thickness  of  the  stratum  of  ore  lying  on  the  latter, 
as  it  is  necessary  to  increase  or  diminish  the  depth  of  the 


49 


SECTIONAL  VIEW  OF  KROM'S  PNEUMATIC  JIG. 


50 


bed  of  ore  operated  upon  according  to  its  coarseness  or 
fineness.  The  finer  the  crushed  ore,  the  thinner  the  stra- 
tum must  be.  The  strap  with  its  screw  fastenings, 
serves  to  prevent  the  roller  attachment  of  the  lever  L 
from  striking  the  body  of  the  trip-wheel,  as  it  falls  from 
each  of  the  cam-shaped  projections,  and  to  regulate  the 
extent  of  movement  of  the  fan.  That  is,  the  strap  must 
in  all  cases  be  so  adjusted  that  the  small  roller  working 
against  the  trip-wheel  shall  not  strike  at  the  foot  of  the 
cam — the  strap  serving  in  this  manner  to  cushion  the 
blow.  Further,  by  tightening  up  or  slacking  off,  by 
means  of  the  screw  fastening,  the  fan  is  carried  in  its 
vibration  through  a  greater  or  less  space,  producing  a 
stronger  or  lighter  puff  of  air.  It  will  be  understood 
that  the  volume  of  the  puff  of  air  required  varies  with 
each  grade  of  ore  operated  upon.  Now,  with  the  strap 
arrangement  alone,  the  puff  of  air  can  be  regulated  to 
the  requirements  of  different  grades  of  ore.  But  as  the 
finer  grades  demand  so  much  less  movement  of  the 
fan  than  do  the  coarser,  it  is  better  to  select  a  trip- 
wheel  from  the  sizes  furnished  which  gives  a  movement 
corresponding  most  nearly  to  that  required,  and  then  to 
make  the  closer  adjustments  by  means  of  the  screw  and 
strap ;  but  the  roller  must  in  no  instance  strike  at  the  foot  of 
the  cam. 

The  novel  features  to  be  particularly  noted  in  this 
separator,  are  as  follows  : 

1st.  The  ore-bed. 

2d.  The  automatic  discharge  rollers. 

3d.  The  fan  for  producing  the  puffs  of  air. 

4th.  The  trip-wheel  and  springs. 

5th.  The  strap  and  adjustable  screw. 

6th.  the  gate  on  the  receiver  H. 

1.  The  ore -bed,  formed  of  wire  gauze  tubes  which  are 
set  in  a  frame  at  short  distances  apart,  to  allow  the  ore 


51 


to  sink  between  them,  is  a  novel  device  for  securing  the 
removal  of  the  concentrated  ore  as  fast  as  the  separation 
on  the  bed  is  completed. 

The  entire  width  of  the  ore-bed  is  4  feet,  and  along 
this  tubes  only  ^  inch  wide  are  set  with  intervening 
spaces  of  T3-g-  to  J-  inch,  consequently  the  total  extent  of 
the  spaces  through  which  the  ore  sinks  is  -^  to  ^  of 
the  entire  ore-bed.  By  this  arrangement  the  downward 
flow  is  very  gradual  between  the  tubes. 

The  automatic  discharge  roller  R, — This  being  driven 
by  the  same  motion  that  works  the  fan,  it  follows  that 
the  concentration  of  the  ore  and  its  discharge  are  effected 
in  concert,  so  that  when  the  speed  of  the  machine 
slackens,  the  concentration  being  less,  the  rate  of  delivery 
is  correspondingly  reduced. 

The  device  for  producing  the  puffs  of  air,  namely — 
A  fan  directly  actuated  by  means  of  a  single  lever,  L, 
is  very  simple  and  effective. 

The  trip-wheel  and  springs  actuatings  the  fan  or 
bellows — The  wheel  by  the  gradual  action  of  its  cams 
throws  back  the  lever  L,  and  consequently  the  fan  or 
bellows-plate  downward  with  a  movement  as  gradual  as 
possible,  and  immediately  the  springs  carry  the  fan 
quickly  upward. 

The  superiority  of  this  device  over  cams,  cranks,  etc., 
is,  that  with  it  a  considerable  variation  of  the  speed  of 
the  machine  does  not  effect  the  quality  of  the  concen- 
tration, but  only  the  quantity. 

If  the  trip-wheel  revolves  slowly  the  number  of  vibra- 
tions of  the  fan  is  less,  but  as  the  spring  causes  the 
upward  movement  of  the  fan  the  puff  of  air  acts  with 
uniform  force,  and  we  thereby  obtain  at  all  speeds  what 
we  may  term  a  concentrating  stroke  of  the  bellows,  as 
the  more  sharply  the  puffs  of  air  are  given  the  more  perfect 
will  be  the  separation. 


52 


In  reference  to  the  strap  and  adjustable  screw,  the 
explanation  already  given  is  sufficient. 

The  gate  on  the  hopper,  H,  compels  the  ore  to  flow 
on  the  ore-bed  as  an  under- current,  and  as  the  puffs  are 
regulated  to  agitate  very  slightly  the  heavy  particles, 
only  the  lighter  portions  will  rise  to  the  surface  and 
be  thrown  over  the  lower  gate,  Gr,  as  tailings,  while  the 
heavy  will  sink  through  the  ore-bed  to  be  discharged  by 
the  roller  R 

This  feature  enables  us  to  concentrate  perfectly  with 
a  very  short  travel  of  the  ore,  or  in  other  words,  to 
employ  a  short  ore-bed  which  is  of  great  advantage. 

By  having  a  short  ore-bed  we  can  extend  what  we 
properly  term  the  width  of  the  bed,  thereby  greatly 
increasing  the  capacity  of  a  machine  of  a  given  size. 
All  other  experimenters  have  caused  the  discharge  of 
the  ore  to  take  place  over  the  narrow  side  of  the 
machine  and  the  travel  of  the  ore  over  the  greater  dis- 
tance. The  reverse  of  this  takes  place  in  this  machine, 
viz. :  the  distance  of  travel  of  the  ore  over  the  bed  is 
only  5  inches,  while  the  line  of  overflow  is  4  feet,  and 
can  be,  at  pleasure,  made  still  greater.  A  short  bed 
enables  us  to  use  a  small  fan,  and  reduces  the  vibrations 
attending  rapid  movements.  A  more  even  and  uniform 
agitation  is  secured  when  the  ore  is  confined  within  nar- 
row limits,  and  more  satisfactory  results  are  obtained. 

Since  I  have  discovered  that  a  short  ore-bed,  of  only 
5  to  6  inches  in  length,  is  no.t  only  sufficient,  but,  in 
fact,  much  superior,  and  that  the  width  of  the  bed  and 
extent  of  overflow  can  accordingly  be  increased,  I  am 
able  so  to  place  the  fan,  and  to  group  in  compact  form 
all  the  working  parts,  and  to  very  considerably  reduce 
the  size  of  the  machine. 

The  puffs  of  air  are  regulated  to  agitate  sufficiently 
the  ore  on  the  bed,  but  should  the  richness  of  the  ore 


53 


increase  during  working  and  too  large  an  amount  collect 
on  the  bed,  the  air  ceases  to  lift  or  agitate  the  material 
as  much,  and  so  a  check  is  furnished  to  prevent  loss  in 
the  tailings.  No  such  check  is  possible  in  water  concen- 
tration, because  water  moves  practically  as  a  solid  and 
carries  all  before  it. 

All  parts  in  this  machine  liable  to  wear  are  manufac- 
tured in  duplicate  and  can  be  cheaply  replaced.  The 
machine  measures  6  feet  in  length  over  all,  3  feet  in 
width,  and  3  feet  10  inches  in  height.  Its  weight,  com- 
plete, is  1,200  pounds,  and  it  is  capable  of  concentrating 
^  ton  per  hour  with  -J-  horse  power. 


KROM'S  PATENTED  LABORATORY  CRUSHER. 

The  foregoing  cut  represents  a  crusher  for  labor- 
atory use. 

In  this  machine  both  jaws  oscillate  on  centers  fixed 
some  distance  from  the  crushing  faces.  The  principal 
feature  is  the  employment  of  segments  of  circles  be- 
tween which  the  ore  is  crushed  on  the  same  principle  as 
rollers  act. 

The  lower  ends  of  the  crushing  plates  are  true  seg- 
ments of  circles,  and  throughout  all  the  movements  of 
the  jaws  they  remain  at  fixed  distances  from  each  other, 
but  the  top  parts  of  the  plates  recede  from  each  other 
with  straight  lines.  The  crusher  can  be  adjusted,  by 
means  of  bolts,  so  as  to  produce  either  fine  or  coarse 
material.  The  crushing  faces  are  made  of  steel,  and  the 
lower  half  of  the  steel  plates  are  hardened.  It  is  the 
only  machine  in  the  market  adapted  for  laboratory  use. 


55 


LABORATORY  JAW  CRUSHER. 


LABORATORY  ROLLERS. 


J 


56 


KROM'S  DRY  KILN. 

Patent   for    this    Dry  Kiln    pending. 


57 


KROM'S  DRY  KILN. 

The  cut,  Fig.  2,  illustrates  my  improved  dry  kiln  for 
drying  ores  after  it  is  broken  by  an  ore  breaker.  The 
cast-iron  plates,  b,  on  which  the  ore  rests  while  drying, 
are  arranged  in  steps,  with  spaces  between  each  step  of 
3  or  4  inches.  These  spaces  allow  the  hot  air  and  gases 
from  the  fire  underneath  to  pass  up  through  the  strata 
of  coarsely  crushed  ore,  as  plainly  indicated  by  the 
arrows. 

The  waste  heat  and  evaporated  moisture  pass  out 
through  the  chimney.  The  plates,  b,  or  steps,  are  placed 
at  an  angle  of  45 p,  but  it  will  be  observed  that  the 
furnace  assumes  an  angle  of  58°.  Therefore  to  maintain 
the  strata  of  ore  of  a  uniform  thickness  it  is  necessary 
to  have  the  check  plates,  a. 

The  distance  between  the  lower  edge  of  these  plates, 
a,  and  the  plates  b,  determines  the  thickness  of  ore 
strata.  This  thickness  can  range  from  6  to  9  inches. 
The  check  plates,  a,  can  be  readily  varied  in  height  by 
means  of  holes  in  the  flanges  which  support  them. 

If  the  location  of  the  mill  site  will  admit  of  so  much 
» 

elevation,  the  plan  shown  in  Fig.  1  will  save  much  labor 
and  expense  in  handling  the  ore.  It  will  be  seen  that 
the  plan  here  suggested  is  for  continuous  and  automatic 
operation. 

Feed  roller  c  is  to  control  and  regulate  the  flow  of 
ore  to  the  crushing  rollers.  It  has  become  necessary  to 
employ  some  means  for  collecting  the  pieces  of  iron  and 
steel  before  they  pass  to  the  pulverizing  machines. 

A  system  of  magnets  is  placed  in  the  shute  a,  z,  d. 

The  arrangement  of  the  magnets  are  more  plainly 
shown  in  Figs.  4  and  5. 


58 


This  dry  kiln  has  decided  advantages  over  the 
revolving  drier.  The  kiln  here  illustrated  requires  no 
power  to  operate  it,  and  the  gentle  flow  of  ore  by 
gravity  over  the  plates  does  not  tend  to  stir  up  dust  or 
create  more  from  abrasion,  and  consequently  no  dust 
chamber  is  required  as  with  cylinder  drier. 

The  fuel  required  to  dry  ore  in  this  kiln  is  the  mini- 
mum amount.  It  is  20  feet  long,  5  feet  wride,  and  holds 
a  strata  of  ore  6  to  8  inches  thick.  The  capacity  of  this 
kiln  may  be  estimated  between  2J  to  5  tons  per  hour. 


V 


Patent  for  this  Dry  Kiln  pending. 


60 


KROM'S  REVOLVING  SCREEN. 

The  cut  on  the  following  page  represents  my  improved 
screen  frame.  The  frame  is  composed  of  light  wrought 
iron  angle-bars,  rolled  expressly  for  the  manufacture  of 
this  screen.  The  form  of  this  bar  is  shown  in  the 
sectional  cut  of  the  rail  marked  k.  The  spiders  which 
carry  these  angle-bars  are  composed  of  a  hub  and 
wrought  iron  spokes.  The  spokes  are  screwed  into  the 
hub  to  a  shoulder  formed  on  the  spoke.  On  the  outer 
end  of  each  spoke  is  another  shoulder  on  which  the 
angle-bars  rest.  All  the  parts  are  made  of  uniform 
dimensions,  and  are  therefore  interchangeable.  The 
angle-bars  hold  the  screen-head  in  the  small  end  by 
means  of  small  bolts. 

The  iron  framework  of  the  screen,  with  its  clamps, 
are  independent  of  the  wooden  frame  on  which  the 
wire  cloth  is  nailed.  To  fasten  the  screen-frame  in 
place  it  is  simply  slid  under  the  clamps,  and  screwed 
down  to  the  angle-bars. 

The  clamps  which  hold  the  screen-frames  to  the  angle- 
bars  are  all  held  up  with  springs,  so  that  when  they  are 
released  the  clamps  are  carried  clear  from  the  screen- 
frame,  and  the  same  is  taken  out  and  put  in  without 
difficulty  by  one  person. 

The  iron  angle-bars  carry  bolts  on  which  are  sliding 
weights  to  jar  the  screen.  On  the  bolt,  next  to  the 
screen,  I  put  a  rubber  cushion,  so  that  a  sharp  blow  is 
given  when  the  weight  falls  from  the  top  of  the  screen, 
and  a  soft  blow  when  the  weight  falls  on  the  lower  side 
of  the  screen.  The  object  of  the  jar  is  to  keep  the 
meshes  of  the  wire-cloth  free  from  particles  of  ore.  I 
also  sometimes  provide  a  casing,  0,  for  the  sliding  weight, 
to  protect  fine  screens  from  damage,  which  may  result 
from  the  breaking  of  the  bolts  on  which  the  weight 


KROM'S  REVOLVING  SCREEN. 

Patent  for  this  Screen  allowed  September  llth,  1885. 


62 


slides.  These  casings  are  made  of  thin  iron  tubes 
screwed  in  a  hub,  similar  to  the  hubs  in  which  the 
spokes  of  the  screen  are  secured.  The  tubes  are  large 
enough  to  clear  the  sliding  or  falling  weight,  and  long 
enough  to  enclose  the  bolt  nearly  its  whole  length.  In 
case  the  bolt  breaks  the  tubes  act  as  a  pocket  to  hold  it. 
This  screen  is  more  complete  and  perfect  in  all  its 
arrangements  and  details  than  any  other  in  the  market. 


YD  07539 


